Thyratrons

ABSTRACT

A multi-gap gradient-grid thyratron in which the discharge gaps are defined between a succession of gradient grids positioned between the anode and the control grid, the gradient-grids being alternately of the long and short type to maintain good insulating between gadient-grids while reducing the size of the thyratron.

United States Patent [1 1 Menown et al.

[ Tl-IYRATRONS [75] inventors: Hugh Menown, Writtle; Eric Jones,

Chelmsford, both of England [73] Assignee: English Electric Valve Company Limited, Chelmsford, Essex, England 22 Filed: Jan. 2, 1974 211 Appl. No.: 430,251

[30] Foreign Application Priority Data Jan. 9, I973 United Kingdom [164/73 [52] U.S. CI 313/195; 313/216 [Sl] Int. Cl. H011 17/12 [58] Field of Search 313/195, 216

[ 51 May 20, 1975 [56] References Cited UNITED STATES PATENTS 3,440,467 4/l969 Menown et al. 3l3/l95 X Primary Examiner-R. V. Rolinec Assistant Examiner-Darwin R. Hostetter Attorney, Agent, or Firm-Baldwin, Wight & Brown [57] ABSTRACT A multi-gap gradient-grid thyratron in which the discharge gaps are defined between a succession of gradient grids positioned between the anode and the control grid, the gradient-grids being alternately of the long and short type to maintain good insulating between gadient-grids while reducing the size of the thyratron.

11 Claims, 5 Drawing Figures PATENTEU 5W2!) 5 F/cz5.

1 THYRATRONS This invention relates to thyratrons and more specifi' cally to so-called multi-gap gradient-grid thyratrons.

As is well known. multi-gap gradient-grid thyratrons consist of two or more discharge gaps between anode and cathode. separated by gradient-grids. There are two species of gradient-grids. One consists of either a single grid electrode or an assembly of two or more closely adjacent parallel-connected electrodes. in which case the gradient-grid is called a short gradientgrid. The other type of gradient-grid consists of two relatively widely spaced electrodes or again two relatively widely spaced assemblies of closely adjacent parallelconnected electrodes. defining a drift space for discharge passing through the gradientgrid, in which case the gradient-grid is termed a long gradient-grid. In the case of a long gradient-grid the voltage between the two electrodes, or the two assemblies of closely adjacent paralIel-connected electrodes forming the gradient-grid need only be sufficient to ensure that the discharge passes through the two electrodes, or two as semblies of electrodes, in sequence. In contrast the main gaps of the thyratron may each be required to withstand as much as 40 kV in operation.

FIGS. 1, 2 and 3 of the accompanying drawings illustrate examples of known prior construction of multigap gradient-grid thyratrons.

Referring to FIG. 1, in this case the thyratron is of the two gap short gradient-grid type. This consists of a ceramic envelope 1, having there within a cathode 2, an anode 3, a control grid 4 and between the control grid 4 and the anode 3 two high voltage gaps 5 and 6, separated by a gradient-grid 7.

Referring to FIG. 2, in this case the thyratron is again of the two gap type, but in this case utilising a long gradient-grid to separate the two high voltage withstanding gaps. The thyratron again consists of a ceramic envelope I, cathode 2, anode 3 and control grid 4. Voltage withstanding gaps S and 6 are separated by a long gradient-grid consisting oftwo spaced electrodes 8 and 9, defining between them a drift space I0.

Referring to FIG. 3, in this case three voltage withstanding gaps ll, 12 and 13 are provided. Gap 11 is separated from gap [2 by a long gradient-grid consisting of two electrodes 14 and IS, with a drift space 17 between them. Gap 12 is separated from gap 13 by a long gradient-grid consisting of two electrodes 18 and I9 with a drift space 20 between them. As before the ceramic envelope is referenced l, the cathode is referenced 2, the anode is referenced 3 and the control grid is referenced 4.

With the known constructions as illustrated in FIGS. I, 2 and 3, the construction of the thyratron having a single gradient-grid (i.e. two voltage withstanding gaps), as shown in FIGS. 1 and 2, is relatively straight forward. Where more than two gaps are required, however. if short gradient-grids are used, it is relatively difficult to provide the insulation clearance necessary to withstand the voltage across the gaps, whilst if long gradient-grids are used (as for example with the construction of FIG. 3) the overall length for a given number of gaps is undesirably great.

The present invention seeks to provide improved multi-gap gradient-grid thyratrons in which the above difficulties of providing satisfactory insulation between the voltage withstanding gaps without the overall length of the structure becoming unduly great is reduced.

According to this invention a multi-gap gradient-grid thyratron is provided having between the control grid and the anode a succession of gradient-grids which are alternately of the short and long type.

Each long gradient-grid may consist of two relatively widely spaced electrodes defining a drift space or it may consist, as previously mentioned, of two relatively widely spaced assemblies of closely adjacent parallelconnected electrodes. Each short gradient'grid may also consist of either a single electrode or an assembly of closely adjacent parallel-connected electrodes.

Preferably the gradient-grids are separated by insulating cylinders, preferably of ceramic.

Preferably again the number of voltage withstanding gaps provided is even and preferably four or more.

FIGS. 1,2 and 3 of the accompanying drawings illustrate examples of known prior construction of multigap gradient-grid thyratrons.

The invention is illustrated in and further described with reference to FIGS. 4 and 5 of the accompanying drawings in which,

FIG. 4 schematically shows one multi-gap gradientgrigl thyratron in accordance with the present invention an FIG. 5 is a sectional view of a practical thyratron in accordance with the present invention.

Referring to FIG. 4, the thyratron again consists of a ceramic envelope 1, the side walls of which are formed by a plurality of ceramic cylinders, between the various electrode connections. Again the cathode is referenced 2, the anode is referenced 3 and the control grid is referenced 4. Between the control grid 4 and the anode 3 is in succession a short gradient-grid 2], a long gradient-grid consisting of two electrodes 22 and 23, delining a drift space 24 and finally a further short gradientgrid 25. This provides four voltage withstanding gaps one 26 between the grid 4 and the short gradient-grid 21, one 27 between the short gradient-grid 21 and the long gradient-grid 22/23, one 28 between the long gradient-grid 22/23 and the short gradienbgrid 25 and one 29 between the short gradient-grid 25 and the anode 3. The cathode 2, grid 4 and anode 3 are extended within the cylindrical ceramic insulators forming the envelope of the tube so as to be in close proximtty to the two short gradient-grids 21 and 25, thereby causing the mean free paths of the molecules of the gas filling to be considerably greater than the gap spacing The two electrodes 22 and 23 forming the long gradi ent-grid, as shown, have applied to them in Operation a potential difference only sufficient to ensure that the discharge builds up through the drift space 24 between them. during gas break down. The four short gaps 26 27, 28 and 29 are insulated by the insulating cerami cylinders which are of length sufficient to withstand the high voltage provided across these gaps. As with known practice the voltage across each gap is of the order of 40 kV in operation.

Referring to the practical example of a thyratron shown in FIG. 5, this shows in detail the construction of a practical example of the thyratron schematically shown in FIG. 4. Within the envelope 1 is a cathode 2 an anode 3 and a control grid 4. Between the control grid 4 and the anode 3 is, in succession, a short gradient-grid 21, a long gradient-grid consisting of two electrodes 22 and 23 with a drift space 24 between them and finally a further short gradient-grid 25. The four voltage withstanding gaps thus provided are referenced 26, 27 28 and 29. The short gradient-grids 2] and 25 each comprise three closely adjacent parallel connected electrodes. The two electrodes 23 and 22 forming the long gradient-grid and the grid 4 each consist of two closely adjacent parallel connected electrodes subreferenced a and b in each case. Each of the parallel connected electrodes a and b have annular openings sub-referenced c and d respectively. The annular openings c which are nearer a voltage withstanding gap lie on a radius which is different (in this case smaller) from the radius on which the annular openings 1] lie. This forces the discharge to travel other than in a straight line. Metallic screens 30 are provided to pre vent discharge from occurring external to the electrode assemblies forming the actual thyratron. The envelope wall of the tube is formed ofshort ceramic cylinders 3t, 32, 33, 34, 35 and 36 separating the various electrodes. The grid referenced 37 is a priming grid not shown in FIG. 4 in order to avoid any undue complication of that schematic diagram. Extending centrally from within the thyratron are two heat conductive members 38 and 39 provided in accordance with the invention in our [1.5. Pat. No. 3,440,467.

We claim:

1. A multi-gap gradient-grid thyratron comprising an envelope, an anode and a cathode within the envelope, a control grid between the anode and the cathode and a succession of gradient-grids between the control grid and the anode, the gradient-grids being alternately of the short and long type.

2. A thyratron as claimed in claim 1 and wherein each long gradient-grid consists of two relatively widely spaced electrodes defining a drift space.

3. A thyratron as claimed in claim 1 and wherein each long gradient-grid consists of two relatively widely spaced assemblies of closely adjacent parallelconnected electrodes.

4. A thyratron as claimed in claim 1 and wherein each short gradient-grid consists of a single electrode.

5. A thyratron as claimed in claim 1 and wherein each short gradient-grid consists of an assembly of closely adjacent parallel-connected electrodes.

6. A thyratron as claimed in claim 1 and wherein the gradient-grids are separated by insulating Cylinders.

7. A thyratron as claimed in claim 6 and wherein the insulating cylinders are of ceramic.

8. A thyratron as claimed in claim I and wherein the number of voltage withstanding gaps provided is even.

9. A thyratron as claimed in claim I and wherein at least four voltage withstanding gaps are provided.

10. A rnulti-gap gradient-grid thyratron comprising,

in combination:

an envelope formed of insulating material and defining an isolated chamber having opposite end portrons;

a cathode disposed in one end portion of said chamber and having a conductor connected thereto and projecting through said envelope at the cathode end thereof, and an anode disposed in the other end portion of said chamber and having a conductor connected thereto and projecting through said envelope at the anode end thereof, and a control grid adjacent said cathode and having a conductor connected thereto and projecting through said envelope adjacent said cathode end thereof, whereby the conductors connected respectively to said anode and to said control grid define a restricted space therebetween; and

at least three other conductors projecting through said envelope within said restricted space. the conductors of one pair of which are closely spaced and a third conductor being widely spaced from said pair and from the conductors connected to said anode and said cathode. a pair of widely spaced long type gradient-grids within said chamber between said anode and said cathode defining a drift space therebetween and a pair of high voltage gaps, and a short type gradient-grid connected to said third conductor and closely spaced with respect to one of said long type gradient-grids to define one of said high voltage gaps and a further high voltage gap, said other conductors being spaced within said restricted space to prevent voltage breakdown between said conductors externally of said envelope.

1]. A multi-gap gradient grid thyratron as defined in claim [0 including a fourth other conductor and a father short type gradient-grid closely spaced to the other of said long type gradient-grids to define therewith the other of said pair of high voltage gaps and a fourth high voltage gap. 

1. A multi-gap gradient-grid thyratron comprising an envelope, an anode and a cathode within the envelope, a control grid between the anode and the cathode and a succession of gradientgrids between the control grid and the anode, the gradient-grids being alternately of the short and long type.
 2. A thyratron as claimed in claim 1 and wherein each long gradient-grid consists of two relatively widely spaced electrodes defining a drift space.
 3. A thyratron as claimed in claim 1 and wherein each long gradient-grid consists of two relatively widely spaced assemblies of closely adjacent parallel-connected electrodes.
 4. A thyratron as claimed in claim 1 and wherein each short gradient-grid consists of a single electrode.
 5. A thyratron as claimed in claim 1 and wherein each short gradient-grid consists of an assembly of closely adjacent parallel-connected electrodes.
 6. A thyratron as claimed in claim 1 and wherein the gradient-grids are separated by insulating cylinders.
 7. A thyratron as claimed in claim 6 and wherein the insulating cylinders are of ceramic.
 8. A thyratron as claimed in claim 1 and wherein the number of voltage withstanding gaps provided is even.
 9. A thyratron as claimed in claim 1 and wherein at least four voltage withstanding gaps are provided.
 10. A multi-gap gradient-grid thyratron comprising, in combination: an envelope formed of insulating material and defining an isolated chamber having opposite end portions; a cathode disposed in one end portion of said chamber and having a conductor connected thereto and projecting through said envelope at the cathode end thereof, and an anode disposed in the other end portion of said chamber and having a conductor connected thereto and projecting through said envelope at the anode end thereof, and a control grid adjacent said cathode and having a conductor connected thereto and projecting through said envelope adjacent said cathode end thereof, whereby the conductors connected respectively to said anode and to said control grid define a restricted space therebetween; and at least three other conductors projecting through said envelope within said restricted space, the conductors of one pair of which are closely spaced and a third conductor being widely spaced from said pair and from the conductors connected to said anode and said cathode, a pair of widely spaced long type gradient-grids within said chamber between said anode and said cathode defining a drift space therebetween and a pair of high voltage gaps, and a short type gradient-grid connected to said third conductor and closely spaced with respect to one of said long type gradient-grids to define one of said high voltage gaps and a further high voltage gap, said other conductors being spaced within said restricted space to prevent voltage breakdown between said conductors externally of said envelope.
 11. A multi-gap gradient-grid thyratron as defined in claim 10 including a fOurth other conductor and a futher short type gradient-grid closely spaced to the other of said long type gradient-grids to define therewith the other of said pair of high voltage gaps and a fourth high voltage gap. 